Trimerising module

ABSTRACT

The present invention relates to the design of trimeric polypeptides using polypeptide structural elements derived from the tetranectin protein family, and their use in rational de novo design and production of multi-functional molecules including the application of the multi-functional molecules in protein library technology, such as phage display technology, diagnostic and therapeutic systems, such as human gene therapy and imaging. The trimeric polypeptides being constructed as a monomer polypeptide construct comprising at least one tetranectin trimerising structural element (TTSE) which is covalently linked to at least one heterologous moiety, said TTSE being capable of forming a stable complex with two other TTSEs; or as an oligomer which is comprised of two monomer polypeptide constructs as mentioned above, and which comprises three TTSEs or a multiplum of three TTSEs, or which is comprised of three monomer polypeptide constructs.

This application is a continuation of U.S. application Ser. No.11/452,434, filed on Jun. 14, 2006, which is a continuation of U.S.application Ser. No. 09/445,576, filed on Jul. 17, 2000, which is anational stage application under 35 U.S.C. §371 of InternationalApplication No. PCT/DK98/00245, filed on Jun. 11, 1998, which claims thebenefit of Denmark Application No. DK0685/97, filed on Jun. 11, 1997,the disclosures of which are explicitly incorporated by referenceherein.

The present invention relates to the design of trimeric polypeptidesusing polypeptide structural elements derived from the tetranectinprotein family, and their use in rational de novo design and productionof multi-functional molecules including the application of themulti-functional molecules in protein library technology, such as phagedisplay technology, diagnostic and therapeutic systems, such as humangene therapy and imaging.

BACKGROUND OF THE INVENTION

Tetranectin is a Ca²⁺-binding trimeric C-type lectin which is present inblood plasma and from the extracellular matrix of certain tissues. Thetetranectin group of proteins comprises tetranectin isolated from manand from mouse and the highly related C-type lectin homologues isolatedfrom the cartilage of cattle (Neame and Boynton, database accessionnumber PATCHX:u22298) and from reef shark (Neame et al., 1992, Neame etal., 1996 and database accession number p26258 and PIR2:A37289).

The mature tetranectin polypeptide chain of 181 amino acid residues isencoded in three exons as shown by molecular cloning andcharacterisation of the gene (Berglund & Petersen, 1992; Wewer &Albrechtsen, 1992). Exon 3 of the human tetranectin gene encodes aseparate functional and structural unit, a single long-form so-calledcarbohydrate recognition domain (CRD), with three intra-chain disulphidebridges. The tetranectin CRD is considered to belong to a distinct classof C-type lectins (Day, 1994) clearly related to C-type lectins bysequence homology, conservation of disulphide topology (Fuhlendorff etal, 1987) and by the presence of an almost conserved suit of amino acidresidues known to be involved in binding of calcium ions.

A published poster (Holtet et al 1996) has proposed tetranectin to be atrimer and that trimerisation is governed by the peptide encoded byexon 1. The peptide encoded by exon 1 was proposed to be “necessary andsufficient to govern trimerisation” whereas the polypeptide encoded byexon 2 was proposed as being “involved in lysine-sensitive binding toplasminogen”.

Tetranectin was first identified as a plasma protein binding toplasminogen by binding to the kringle-4 domain of plasminogen. Recentunpublished results (Graversen et al., manuscript for PNAS) proves (1)that the site in tetranectin involved in binding to plasminogen residesentirely in the CRD-domain (encoded by exon 3), (2) that binding iscalcium sensitive, and (3) that the kringle-4 binding site intetranectin overlaps the putative carbohydrate binding site of the CRDdomain. Hence, there is now surprising definitive evidence that TN exons1 and 2, i.e. the trimerisation unit in TN does not exhibit anyplasminogen-binding affinity. Accordingly, an artificial proteincontaining a TTSE unit as part of its architecture is not expected tointeract with plasminogen or plasmin due to properties inherited fromtetranectin.

Tetranectin has also been reported to bind to sulfated polysaccharideslike heparin (Clemmensen (1989) Scand J. Clin. Lab. Invest. vol49:719-725). We have new results showing that the CRD domains oftetranectin are not involved in this protein-polysaccharide interaction.In fact, the site in tetranectin is located in the N-terminal region ofexon 1 and may be abolished by removal or mutagenis of N-terminal lysineresidues (Graversen et al., manuscript), processes that do not inhibittrimerisation. TTSEs that include most or all of TN exon 1 thereforeconfer an affinity for sulfated polysaccharides to any designed proteinwhich encompasses such a TTSE as part of its structure. If desired,however, this affinity can be reduced or abolished by N-terminaltruncation or mutagenesis of lysine residues in the part of the TTSEthat corresponds to the N-terminal 8-10 amino acid residues of exon 1(Graversen et al., unpublished).

With respect to gene therapy which is also within the scope of thepresent invention, there is only a limited number of basic strategiesfor gene therapy which show some promise in preclinical models so far.The two major strategies e.g for the treatment of malignant tumors arecytokine-gene aided tumor vaccination and selective prodrug activation.Whereas the first strategy relies on the strong immunostimulatory effectof a relatively small number of genetically modified cytotoxic T cellsor tumor cells, the second one is based on conversion of a nontoxicprodrug into a toxic product by an enzyme-encoding gene where the toxiceffect is exerted also on non-transduced dividing tumor cells due to aso-called bystander effect. Alternatively, strategies can be envisagedwhere the malignant phenotype of a cell is reversed by eitherinactivating an oncogene or reestablishing an inactivated tumorsuppressor gene. In both cases, highly efficient gene transfer to thecells in a tumor is required. Although high efficiencies of genetransfer can be obtained in vitro and even in vivo under certaincircumstances, correction of the malignant phenotype by reversing themajor oncogenic change in the tumor cells is unlikely to result innormal cells. Thus, selective induction of tumor cell death by use ofthe present invention would be preferable, and the development ofmethods enabling such induction will be of great importance.

A major problem in connection with the gene therapy is the incorporationof foreign material into the genome. Viruses, however, have only beenpartially successful in overcoming this problem. Hence the initialefforts at gene therapy are still directed towards engineering virusesso that they could be used as vectors to carry therapeutic genes intopatients. In the still very immature in vivo method of somatic genetherapy, where a vector could be injected directly into the bloodstream,or more preferably by transmucosal delivery, the present invention maybe utilized due to the surprising number of ways the gene therapy may betargeted.

For many gene-therapy applications in the future, it is probable that asynthetic hybrid system will be used that incorporates engineered viralcomponent for target-specific binding and core entry, immunosuppressivegenes from various viruses and some mechanism that allows site-specificintegration, perhaps utilizing AAV sequences or an engineered retroviralintegrase protein. In addition, regulatory sequences from the targetcell itself will be utilized to allow physiological control ofexpression of the inserted genes. All these components would beassembled in vitro in a liposome-like formulation with additionalmeasures taken to reduce immunogenicity such as concealment by PEG

As mentioned, one of the current problems in gene therapy is theefficient delivery of nucleic acids to as many as possible of a specificpopulation of cells in the body, and it is often not possible to finde.g. an appropriate viral vector that will find that particular cellpopulation efficiently and selectively (Review on aspects of genetherapy: Schaper, W & Ito, W. D. Current Opinion in Biotechnology, 1996,vol. 7, 635-640. Nature Biotechnology 1998 vol 16 is an entire volumededicated to protein- and gene delivery).

Given the possibility of in vitro generation of a human antibody againstvirtually any target antigen by phage technology, it follows that TTSES,where one of the subunits is modified with a membrane integrating orassociating entity, may be used as a practicable tool for generating aviral, bacterial or preferentially artificially assembled lipomalvehicle that will allow selective delivery of the contained material byinfection or transfection of any cell population to which such aspecific antibody may be generated. Moreover vehicles may, with the useof TTSEs, be individualised by selection of patient specific antibodiesor by assembling TTSE units conjugated with scFvs selected from anensemble of antibodies selected by the particular markers of thedisease.

SUMMARY OF THE INVENTION

It has surprisingly been found by the present inventors that the humantetranectin polypeptide (and derivatives thereof) is capable of formingvery stable trimers which have a number of advantageous characteristicsand uses. Notably, the tetranectin molecule includes a trimerisingstructural element which can be used as carrier of other chemicalentities, thereby providing a carrier molecule of a hitherto unseenversatility.

Prior published knowledge in the field of providing trimerisingpolypeptides of choice includes the disclosure in WO 95/31540 by Hoppeand Reid which describes a trimerisation module derived from collectincoiled coil structures and its application in engineering ofartificially trimerised proteins. Several interesting areas ofapplication are common to that patent publication and to the presentdisclosure. However, in several ways the properties of the trimerisationmodules derived from the tetranectin protein family as disclosed hereinare markedly different in fundamental architecture and representsurprisingly improved properties in comparison with the collectintrimerisation unit:

(1) Although the spatial structures of both trimerisation modules at asuperficial level appear as similar in that both are ternary coiled coilstructures of roughly equivalent spatial size the structural basis foradopting this spatial configuration is markedly distinct between the twogroups of proteins. In fact, it is so distinct that the common beliefprior to the work of Holtet et al. on cross-linking of human tetranectin(Holtet et al., 1996) was that this family of proteins were tetrameric(hence the name). Accordingly, the sequences of the tetranectin familyof trimerisation modules does not conform to the declared common motifdelineated for the collectin family (WO 95/31540, page 8).

(2) The thermal stability of the tetranectin trimerisation module (asshown in the examples) is such that the trimer can be shown to existeven at about 60° C. (Example 4, trimerised tetranectin) or at about 70°C. (Example 3, trimerised ubiquitin), whereas a collectin trimer unitfalls apart at about 50-55° C. (WO 95/31540, Example 1, page 36therein).

(3) Whereas it remains uncertain whether the collectin trimerisationdomain possibly allows attachment of fusion partners at C-terminal endsof the trimerisation module, and whereas no example has been reported ofsuccessful or claimed successful attachment of a foreign protein (exceptfor the GST fusion partner) to the N-terminal region of the collectintrimerisation module, the information disclosed herein demonstrates thatthe tetranectin trimerisation module is more versatile in that is allowsattachment of foreign proteins to either, as well as to both, terminusor termini simultaneously (Examples 1-4). This has importantconsequences as the tetranectin trimerisation module may be deployed toconstruct molecules that are able to interact (each end with a bindingvalency up to 3) simultaneously with two bulky interaction partners likee.g. cell surfaces.

(4) The virtual absence of subunit exchange between monomers of a trimerthat has been trimerised using the tetranectin trimerisation modulesdisclosed herein is by first principles of thermodynamics correlatedwith the surprisingly high thermal stability of the complex. It willhence be apparent that the advantages inherent to the “pick-and-mix”applications of the technology, as disclosed herein, may be used to muchgreater advantage because of the much longer shelf life expected for theheterofunctional products of the present invention.

The polypeptide constructs CIIH6FXTN123, H6FXTN123, H6FXTN12, andH6FXTN23 which all involve parts of the tetranectin molecule havepreviously been prepared (cf. e.g. WO 94/18227) but these constructshave all been provided with a view to facilitating expression and/orpurification of the tetranectin derived moiety of the constructs. To thebest of the inventors' knowledge no publications exist which reports anyuse of tetranectin derivatives as “building blocks” to which otherchemical moieties advantageously could be coupled.

Hence, in its broadest aspect the present invention relates to a monomerpolypeptide construct comprising at least one tetranectin trimerisingstructural element (hereinafter designated a TTSE) which is covalentlylinked to at least one heterologous moiety, said TTSE being capable offorming a stable complex with two other TTSEs, with the proviso that theheterologous moiety is different from any of the fusion proteinsCIIH6FXTN123, H6FXTN123, H6FXTN12, H6FXTN23, the sequences of which areshown in SEQ ID NOs: 24-27. It is preferred that the heterologous moietyis one which does not exclusively facilitate expression and/orpurification of the monomer polypeptide construct.

The invention further relates to oligomeric molecules comprised of atleast two of such monomer polypeptide constructs, and the invention alsorelates to methods of preparing the monomer polypeptide constructs andthe oligomers. The invention further relates to a kit comprising monomerpolypeptide constructs in separate packages, ready for use in a“pick-and-mix” approach for use of the monomers. This pick and mixapproach is for use in therapeutic as well as for dianostic use. Eg.having a tumor with a known and specific epitope to which an antibody isavailable. The kit may then comprise a first TTSE conjugated to anrelevant antibody, a second component which may comprise af TTSE coupledto an imaging compound. In a second aspect the second component maycomprise a drug or a prodrug relevant for treating the tumor. In a stillfurther aspect a third TTSE component being a monitoring compound, e.g.indicative of the progress of the targeting.

As is clear from this illustration the present invention relates to alarge amount of combinations allowing an individual design for a largenumber of circumstances.

Finally, the invention also pertains to fragments which include nucleicacid sequences which encode the monomer polypeptide constructs, as wellas to vectors and cells containing these nucleic acid fragments.

LEGENDS TO THE FIGURES

FIG. 1: Amino acid sequence of the amino terminal region of tetranectin.

Amino acid sequence (in one letter code) from E1 to L51 of tetranectin(SEQ ID NO: 7). Exon 1 comprises residues E1 to D16 and exon 2 residuesV17 to V49, respectively. The alpha helix extends beyond L51 to K52which is the C-terminal amino acid residue in the alpha helix.

FIG. 2: Alignment of the amino acid sequences of the trimerisingstructural element of the tetranectin protein family.

Amino acid sequences (one letter code) corresponding to residue V17 toK52 comprising exon 2 and the first three residues of exon 3 of humantetranectin (SEQ ID NO: 7); murine tetranectin (Sørensen et al., Gene,152: 243-245, 1995); tetranectin homologous protein isolated fromreef-shark cartilage (Neame and Boynton, 1992, 1996); and tetranectinhomologous protein isolated from bovine cartilage (Neame and Boynton,database accession number PATCHX:u22298). Residues at a and d positionsin the heptad repeats are listed in boldface. The listed consensussequence of the tetranectin protein family trimerising structuralelement comprise the residues present at a and d positions in the heptadrepeats shown in the figure in addition to the other conserved residuesof the region. “hy” denotes an aliphatic hydrophobic residue.

FIG. 3: Construction of the expression plasmids pTH6FXtripa andpTH6FXtripb.

The amplified DNA fragments tripa and tripb harbouring the tetranectinamino acid sequence (SEQ ID NO: 7) from E1 to T48 and E1 to K52,respectively, fused in the 5′ end to nucleotide sequences encoding aFX_(a) cleavage site IQGR (SEQ ID NO: 4) and the recognition sites forthe restriction endonucleases BglII and KpnI, were cut with therestriction enzymes BclI and HindIII and ligated into the BamHI andHindIII sites of the expression plasmid pT7H6 (Christensen et al., 1991)using standard procedures.

FIG. 4: Predicted amino acid sequence of the fusion proteins H6FXtripa(SEQ ID NO: 28) and H6FXtripb (SEQ ID NO: 29) encoded by the expressionplasmids pTH6FXtripa and pTH6FXtripb, respectively.

FIG. 5: Construction of the expression plasmids pTH6FXTN123 andpTCIIH6FXTN123.

The amplified DNA fragment corresponding to the full length, maturetetranectin monomer (SEQ ID NO: 7) from E1 to V181 fused in the 5′ endto nucleotide sequences encoding a FX_(a) cleavage site IEGR (SEQ ID NO:10) was cut with the restriction enzymes BamHI and HindIII and ligatedinto the corresponding sites of the expression plasmids pT7H6(Christensen et al., 1991) and pTCIIH6 using standard procedures.pTCIIH6 was derived from pT7H6 by substitution of the NdeI-HindIIIfragment of pT7H6 with the NdeI-HindIII fragment of pLcII (Nagai andThøgersen, 1987) encoding the first 32 residues of the lambda cIIprotein MVRANKRNEALRIESALLNKIAMLGTEKTAEG (SEQ ID NO: 11) fused in the 3′end to a nucleotide sequence encoding the H6 sequence GSHHHHHHGS(SEQ IDNO: 12).

FIG. 6: Predicted amino acid sequence of the fusion proteins H6FXTN123(SEQ ID NO: 25) and CIIH6FXTN123 (SEQ ID NO: 24) encoded by theexpression plasmids pTH6FXTN123 and pTCIIH6FXTN123, respectively.

FIG. 7: Construction of the expression plasmids pTH6FXTN12, pTH6FXTN23,and pTH6FXTN3.

The amplified DNA fragments corresponding to the tetranectin derivativesTN12 and TN3 from E1 to V49 and A45 to V181, respectively (SEQ ID NO: 7)fused in the 5′ end to nucleotide sequences encoding the FX_(a) cleavagesite IEGR (SEQ ID NO: 10) was cut with the restriction enzymes BamHI andHindIII and ligated into the corresponding sites of the expressionplasmids pT7H6 (Christensen et al., 1991) using standard procedures. Theamplified DNA fragment corresponding to the tetranectin derivative TN23from V17 to V181 (SEQ ID NO: 7) fused in the 5′ end to nucleotidesequences encoding the FX_(a) cleavage site IQGR (SEQ ID NO: 4) was cutwith the restriction enzymes BamHI and HindIII and ligated into thecorresponding sites of the expression plasmids pT7H6 (Christensen etal., 1991) using standard procedures.

FIG. 8: Predicted amino acid sequence of the fusion proteins H6FXTN12(SEQ ID NO: 26), H6FXTN23 (SEQ ID NO: 27), and H6FXTN3 (SEQ ID NO: 30)encoded by the expression plasmids pTH6FXTN12, pTH6FXTN12, respectively.

FIG. 9: Gel filtration analysis of TN123, TN23, and TN3

Analytical gel filtration of the recombinant tetranectin derivativesTN123, TN23, and TN3 were performed on a Superose 12 HR 10/30 column(Pharmacia, Sweden) with a total volume of 25 ml in 100 mM NaCl and 50mM Tris-HCl pH 8 and a flow rate of 0.2 ml/min. Vertical bars at peakmaxima identify elution profiles for each of the three proteins.

FIG. 10: Cross-linking analysis of TN123 and CIIH6FXTN123.

Samples of TN123, CIIH6FXTN123 and mixtures of both were incubated withDMSI and analyzed by SDS-PAGE (12% gel). p Before addition of DMSI,protein mixtures were subjected to subunit exchange by incubation at 70°C. for varying length of time. Protein marker of 94, 68, 43 and 30 kDa,top to bottom (lane M). CIIH6FXTN123 fusion protein (lane 1). TN123(lane 2). DMSI treated CIIH6FXTN123 (lanes 3 and 6). DMSI-treated TN123(lane 4). Identical samples of DMSI treated mixtures of CIIH6FXTN123 andTN123 without heat exposure (lanes 5 and 7) and heat treated for 2.5sec, 15 sec, 2.5 min. and 10 min., respectively, before treatment withDMSI (lanes 8-11).

FIG. 11: Cross-linking analysis of the recombinant tetranectinderivatives TN123, TN23, TN3, and H6FXTN12.

The recombinant proteins TN123, TN23, TN3, H6FXTN12 or mixtures of TN123and each of the other were analyzed by SDS-PAGE. Protein marker of 94,68, 43, 30, 20, and 14.4 kDa, top to bottom (lane M). TN123 cross-linkedwith DMSI (lane 1). TN123 and H6-rTN12 cross-linked with DMSI withoutand with heat treatment at 70° C. for two min. (lanes 2 and 3). H6FXTN12cross-linked with DMSI (lanes 4 and 5). Mixture of TN123 and H6FXTN12,no cross-linking (lane 6). Cross-linking of TN123 and TN23 without andwith heat treatment at 70° C. for two min. (lanes 7 and 8).Cross-linking of TN23 (lane 9). Mixture of TN123 and TN23 withoutcross-linking (lane 10). TN123 cross-linked by DMSI (lane 11).Cross-linking of TN123 and TN3 without and with heat treatment for twomin. (lanes 12 and 13). Cross-linking of TN3 (Lane 14). Mixture of TN123and TN3, no cross-linking (lane 15).

FIG. 12: Cross-linking based analysis of the trimer thermal stability.

In parallel experiments TN123 and the fusion protein H6FXtripb-UB (SEQID NO: 31) were cross-linked with DMSI at different temperatures and thesamples analyzed by SDS-PAGE. Protein marker of 94, 68, 43, 30, 20, and14.4 kDa, top to bottom (lane M). TN123 without cross-linking (lane 1).TN123 cross-linked with DMSI for 15 min. at 37° C., 50° C., 60° C., and70° C. (lanes 2 to 5), respectively. The fusion protein H6FXtripb-UB(SEQ ID NO: 31) without cross-linking (lane 6). H6FXtripb-UBcross-linked with DMSI for 15 min. at 37° C., 50° C., 60° C., and 70° C.(lanes 7 to 10), respectively and H6FXtripb-UB incubated at 70° C. for15 min. (lane 11).

FIG. 13: Construction of the expression plasmid pTH6FXtripb-UB.

The amplified DNA fragment comprising the nucleotide sequence (SEQ IDNO:16) encoding the ubiquitin amino acid sequence (SEQ ID NO: 19) fromQ2 to G76 was cut with the restriction enzymes BclI and HindIII andligated into the BamHI and HindIII sites of the expression plasmidpT7H6FXtripb (Example 1) using standard procedures.

FIG. 14: Predicted amino acid sequence of the fusion proteinH6FXtripb-UB (SEQ ID NO: 31) encoded by the expression plasmidpTH6FXtripb-UB.

FIG. 15: Construction of the expression plasmid pTH6FXscFV (CEA6)tripb.

The DNA fragment, amplified with the primer pair SEQ ID NOs: 21 and 22,comprising the nucleotide sequence SEQ ID NO: 20 encoding the singlechain antibody CEA6, scFV (CEA6), amino acid sequence from Q1 to A261was cut with the restriction enzymes BamHI and KpnI and ligated into theBglII and KpnI sites of the expression plasmid pT7H6FXtripb (Example 1)using standard procedures.

FIG. 16: Predicted amino acid sequence of the fusion proteinHGFXscFV(CEA6)tripb encoded by the expression plasmidpH6FXscFV(CEA6)tripb.

FIG. 17: Construction of the expression plasmid pTH6FXtripbscFX(CEA6).

The DNA fragment, amplified with the primer pairs having SEQ ID NO: 21and 23, comprising the nucleotide sequence (SEQ ID NO: 20) encoding thesingle chain antibody CEA6, scFV (CEA6), amino acid sequence from Q1 toA261 was cut with the restriction enzymes BamHI and HindIII and ligatedinto the BamHI and HindIII sites of the expression plasmid pT7H6FXtripb(Example 1) using standard procedures.

FIG. 18: Predicted amino acid sequence of the fusion proteinH6FXtripbscFv(CEA6) encoded by the expression plasmidpH6FXtripbscFv(CEA6).

FIG. 19: Construction of the expression plasmidpTH6FXscFv(CEA6)tripbscFX(CEA6).

The DNA fragment, amplified with the primer pair SEQ ID NO: 21 and 23,comprising the nucleotide sequence (SEQ ID NO: 20) encoding the singlechain antibody CEA6, scFV (CEA6), amino acid sequence from Q1 to A261was cut with the restriction enzymes BamHI and HindIII and ligated intothe BamHI and HindIII sites of the expression plasmidpT7H6FXscFv(CEA6)tripb (Example 4) using standard procedures.

FIG. 20: Predicted amino acid sequence of the fusion proteinH6FXscFv(CEA6)tripbscFv(CEA6) (SEQ ID NO: 34) encoded by the expressionplasmid pH6FXscFv(CEA6)tripbscFv(CEA6).

FIG. 21: Cross-linking analysis of the H6FXtripbscFv(CEA6) fusionprotein (SEQ ID NO: 33).

In parallel experiments the fusion proteins H6FXtripbscFv(CEA6) (SEQ IDNO: 33) and TN123 were cross-linked at room temperature for 30 min. with0 mg/ml, 0.5 mg/ml, 1.0 mg/ml, 1.5 mg/ml, and 2.0 mg/ml of DMSI,respectively. Lane 1: H6FXtripbscFv(CEA6) without DMSI,H6FXtripbscFv(CEA6) with 0.5 mg/ml DMSI (lane 2), H6FXtripbscFv(CEA6)with 1.0 mg/ml DMSI (lane 3), H6FXtripbscFv(CEA6) with 1.5 mg/ml DMSI(lane 4) and H6FXtripbscFv(CEA6) with 2.0 mg/ml DMSI (lane 5). Proteinmarker of 94, 68, 43, 30, 20, and 14.4 kDa, top to bottom (lane M). Lane6: TN123 without DMSI, TN123 with 0.5 mg/ml DMSI (lane 7), TN123 with1.0 mg/ml DMSI (lane 8) TN123 with 1.5 mg/ml DMSI (lane 9) and TN123with 2.0 mg/ml DMSI (lane 10).

DETAILED DISCLOSURE OF THE INVENTION

The term “trimerising structural element” (TTSE) used in the presentdescription and claims is intended to refer to the portion of apolypeptide molecule of the tetranectin family which is responsible fortrimerisation between monomers of the tetranectin polypeptide. The termis also intended to embrace variants of a TTSE of a naturally occurringtetranectin family member, variants which have been modified in theamino acid sequence without adversely affecting, to any substantialdegree, the trimerisation properties relative to those of the nativetetranectin family member molecule. Specific examples of such variantswill be described in detail herein, but it is generally preferred thatthe TTSE is derived from human tetranectin, murine tetranectin, C-typelectin of bovine cartilage, or C-type lectin of shark cartilage.Especially preferred is monomer polypeptide constructs including atleast one TTSE derived from human tetranectin.

The 49 residue polypeptide sequence encoded by exons 1 and 2 oftetranectin (FIG. 1) appears to be unique to the tetranectin group ofproteins (FIG. 2) as no significant sequence homology to other knownpolypeptide sequences has been established. In preparation forexperimental investigations of the architecture of tetranectin acollection of recombinant proteins was produced, the collectionincluding complete tetranectin, the CRD domain (approximatelycorresponding to the polypeptide encoded by exon 3), a productcorresponding to the polypeptide encoded by exons 2+3, a productcorresponding to exons 1+2 (Holtet et al., 1996; Example 2). As detailedin Example 2 we now know differently: tetranectin is indeed a trimer,but the exon 2 encoded polypeptide is in fact capable of effectingtrimerisation by itself as evidenced by the observation that therecombinant protein corresponding to exons 2+3 is in fact trimeric insolution.

3D-structure analysis of crystals of full-length recombinant tetranectin(Nielsen et al., 1996; Nielsen, 1996; Larsen et al., 1996; Kastrup,1996) has shown that the polypeptide encoded in exon 2 plus threeresidues encoded in exon 3 form a triple alpha helical coiled coilstructure.

From the combination of sequence and structure data it becomes clearthat trimerisation in tetranectin is in fact generated by a structuralelement (FIG. 2), comprising the amino acid residues encoded by exon twoand the first three residues of exon 3 by an unusual heptad repeatsequence, that apparently is unique to tetranectin and other members ofits group: This amino acid sequence (FIG. 2) is characterised by twocopies of heptad repeats (abcdefg) with hydrophobic residues at a and dpositions as are other alpha helical coiled coils. These two heptadrepeats are in sequence followed by an unusual third copy of the heptadrepeat, where glutamine 44 and glutamine 47 not only substitute thehydrophobic residues at both the a and d position, but are directlyinvolved in the formation of the triple alpha helical coiled coilstructure. These heptad repeats are additionally flanked by twohalf-repeats with hydrophobic residues at the d and a position,respectively.

The presence of beta-branched hydrophobic residues at a or d positionsin alpha helical coiled coil are known to influence the state ofoligomerisation. In the tetranectin structural element only oneconserved valine (number 37) is present. At sequence position 29 intetranectin no particular aliphatic residue appears to be preferred.

In summary, it is apparent that the triple stranded coiled coilstructure in tetranectin to a large extent is governed by interactionsthat are unexpected in relation to those characteristic among the groupof known coiled coil proteins.

The TTSEs form surprisingly stable trimeric molecules. (Examples 2, 3and 4). The experimental observations, that (1) a substantial part ofthe recombinant proteins exists in the oligomeric state of—and can becross-linked as—trimeric molecules even at 70° C. and (2) that exchangeof monomers between different trimers can only be detected afterexposure to elevated temperature are evidence of a extremely highstability of the tetranectin trimerising structural element. Thisfeature must be reflected in the amino acid sequence of the structuralelement. In particular, the presence and position of the glutaminecontaining repeat in the sequential array of heptad repeats is, togetherwith the presence and relative position of the other conserved residuesin the consensus sequence (FIG. 2), considered important for theformation of these stable trimeric molecules. For most practical usesthe cysteine residue 50 should be mutagenized to serine, threonine,methionine or to any other amino acid residue in order to avoidformation of an unwanted inter-chain disulphide bridge, which eventuallywould lead to uncontrolled multimerisation, aggregation andprecipitation of a polypeptide product harbouring this sequence.

In particular in conjunction with the trimer-stabilising exon 1 encodedpolypeptide (tetranectin residues 1 to 16, see Example 2), thetetranectin trimerising structural element is a truly autonomouspolypeptide module retaining its structural integrity and propensity togenerate a highly stable homotrimeric complex whether it is attached ornot by a peptide bond at either or at both termini to other proteins.This unique property is demonstrated in the accompanying examples, whichprovide experimental proof, that polypeptide sequences derived fromheterologous proteins may readily be trimerised when joined as fusionproteins to the tetranectin trimerising structural element. This remainsvalid irrespective of whether the heterologous polypeptide sequences areplaced amino-terminally or carboxy-terminally to the trimerising elementallowing for the formation of one molecular assembly containing up tosix copies of one particular polypeptide sequence or functionalentities, or the formation of one molecular assembly containing up tosix different polypeptide sequences, each contributing their individualfunctional property.

Since three TTSEs of naturally occurring human tetranectin forms up atriple alpha helical coiled coil, it is preferred that the stablecomplex formed by the TTSEs of the invention also forms a triple alphahelical coiled coil.

The “tetranectin family” are polypeptides which share the consensussequence shown in FIG. 2 or a sequence which are homologous at sequencelevel with this consensus sequence. Hence, monomer polypeptideconstructs of the invention are preferred which comprise a polypeptidesequence which has at least 68% sequence identity with the consensussequence shown in FIG. 2, but higher sequence identities are preferred,such as at least 75%, at least 81%, at least 87%, and at least 92%.

By the term “heterologous moiety” is herein meant any chemical entitywhich can be linked covalently to a TTSE and to which the TTSE is notnatively covalently bound. Hence, the heterologous moiety can be anycovalent partner moiety known in the art for providing desired binding,detection, or effector properties. The heterologous moiety can be aligand binding structure such as a receptor molecule or the ligandbinding part of a receptor molecule, an antibody, an antigen bindingantibody fragment, or a molecule having antibody characteristics such ase.g. the “diabodies” described in EP-A-0 672 142, or other ligandbinding molecules such as avidin or streptavidin, or a lectin; a toxinsuch as ricin; a detectable label such as a fluorescence labelledmolecule, a radioactively labelled molecule, an enzymatically labelledmolecule; an in situ activatable substance, such as a molecule which canbe induced by a magnetic field or by radiation to be radioactively orchemically active; an enzyme such as a peroxidase; a radioactive moietysuch as a γ-, α-, β⁻-, or β⁺-emitting molecule, e.g. a moleculecomprising one or more radioactive isotopes selected from ¹⁴C, ³H, ³²P,³³P, 25S, 38S, ³⁶Cl, ²²Na, ²⁴Na, ⁴⁰K, ⁴²K, ⁴³K, and any isotopesconventionally utilized for the purposes of facilitating detection ofprobes or the purposes of providing localized radiation so as to effectcell death; a cytokine such as an interferon or a leukotriene; PNA; anon-proteinaceous polymer such as a polymeric alkaloid, 11.apolyalcohol, a polysaccharide, a lipid and a polyamine; a photocross-linking moiety, i.e. a chemical entity which effects cross-linkingupon photo-activation; and a group facilitating conjugation of themonomer polypeptide construct to a target.

The heterologous moiety is preferably covalently linked to the TTSE byvia a peptide bond to the N- or C-terminus of the TTSE peptide chain,via a peptide bond to a side chain in the TTSE or via a bond to acysteine residue, but any way of coupling covalently heterologousmaterial to a polypeptide chain will be useful. The skilled person willknow of such possibilities, e.g. by consulting the teachings of WO95/31540 in this regard which are hereby incorporated by reference.

However, one interesting aspect of the invention relates to a monomerpolypeptide construct of the invention comprising two heterologousmoieties which are linked via peptide bonds to the N- and C-terminus,respectively. This approach introduces a number of possibilities interms of e.g. linking larger entities with oligomers of the invention byhaving specific activities coupled to each end of the monomers (asexplained in detail below, the oligomers of the invention may alsoutilise a version of this principle, where e.g. one N-terminus and oneC-terminus of an oligomer are linked via peptide bonds to independentheterologous moieties).

In general, a complex between two or three monomers are described in thefollowing way: three monomers having one TTSE each forms a trimerdesignated (1+1+1), whereas a dimer formed between a monomer with twoTTSEs and a monomer with one TTSE is designated (1+2). Other (undesired)trimers can of course be formed, e.g. (2+2+1), where two TTSEs are not“in use”, but it is preferred that the oligomers of the invention useall of their available TTSEs during complex formation. It should also benoted that the term “monomer polypeptide construct” is meant todesignate a single polypeptide chain which may or may not havenon-peptide groups coupled covalently to the polypeptide chain, whereas“dimeric polypeptide” or “dimer”, “trimeric polypeptide” or “trimer” and“oligomer” (i.e. a dimer or trimer) in the present context are meant todesignate non-covalent complexes of monomer polypeptide constructs.I.e., the traditional definitions of monomers and multimers do not applyin the present specification and claims.

The TTSE as exemplified by exon 2 or exons 1 and 2 of human tetranectin,preferably so modified to allow only hetero-trimerisation betweendissimilar (1+1+1) or (1+2) (cf. the below discussion) subunits may bedeployed as a general affinity mediator, which can be coupled chemicallyto each member of a selection of target molecules. After suchconjugation with TTSE the target molecules may be homo- orheterotrimerised as desired for any application. Similar deployment ofdimerisation, using as one partner a polypeptide harbouring two TTSEsequences in-line, separated by a linker sequence of suitable length andcharacter, may bet yet more advantageous, as in such case absolutecontrol of stoichiometry in complex formation would be possible. Thus,an important embodiment of the invention is a monomer polypeptideconstruct of the invention comprising 2 TTSEs which are covalentlylinked by a spacer moiety which allows both of the 2 TTSEs to take partin complex formation with a third TTSE not being part of the monomerpolypeptide construct, but equally important is the embodiment of theinvention where the monomer polypeptide construct comprises one singleTTSE, so as to allow trimerisation between three monomers and henceproviding the optimum degree of versatility with respect to the numberof functional units which can be easily incorporated into one singlecomplex.

In the embodiments where two TTSEs are present in the same monomer it ispreferred that the spacer moiety has a length and a conformation whichfavours complex formation involving both of the two TTSEs which arecovalently linked by the spacer moiety. In this way, problems arisingfrom undesired formation of trimers of the formats (2+1+1), (2+2+2), and(2+2+1) (wherein only one TTSE of each monomer participates in complexformation) can be diminished. Design and preparation of suitable spacermoieties are known in the art and are conveniently effected by preparingfusion polypeptides having the format TTSE¹-Spacer-TTSE², where thespacer moiety is a polypeptide fragment (often a relatively inert one),so as to avoid undesired reactions between the spacer and thesurroundings or the TTSEs.

One typical scenario, where such modification may be advantageous is thecase of immunological detection where a chemical conjugate of anantibody with enzymes such as peroxidase is used for in situ stainingpurposes in tissue or on western blots.

A similar, but yet different, application example would be thedeployment of TTSE to mediate conjugation of e.g. alkaline phosphataseand an oligonucleotide which would allow in situ identification of agiven mRNA in a tissue sample concurrently with identification of anyother mRNA molecule e.g. by interconnection of a second appropriateoligonucleotide and a signalling/visualisation molecule using e.g. thebiotin—avidin/streptavidin affinity pair for conjugation. The point ofhaving two or more selective affinity systems available for conjugatingoligonucleotide probes and detector molecules is that as many differentsequences may be detected simultaneously as there are affinity setsavailable.

In terms of chemistry required to exploit TTSE as a conjugatingaffinity-contributing agent, the peptide corresponding to exon 2 willhave a sufficient affinity for most purposes, but incorporation of all,or some segment of the exon 1 polypeptide will serve to increaseaffinity and stability. The properties of tetranectin mutants in whichmany of hydrophilic (e.g. lys and glu) residues that are largelyexterior in the coiled coil structure have been replaced with alanineappear similar to the native protein, suggesting that is indeed possiblewithout interfering very much with stability of the trimeric structureto replace all glu, asp and lys residues by a combination of gln, asn,arg or ala, and thereby generate a sequence that, as an N-terminallyblocked synthetic peptide, would be very easy to convert into achemically stable active-ester component, e.g. an N-hydroxy succinimideester of an acetylated peptide, that could react with (and therebycouple to) any exposed lysine side chain in a target molecule ofinterest. Such peptide synthesis, activation and coupling chemistry willbe readily designed and applied by a person skilled in the art ofpeptide chemistry, as will indeed any other conjugation chemistry, likethe attachment and use of photo-activatable moieties like e.g. phenylazides.

In conclusion, it seems that the most important structure in native TTSEis the consensus sequence shown in FIG. 2, and that large variations inthe polypeptide chain may be allowed. Hence, one advantageous embodimentof the monomer polypeptide construct of the invention is one where atleast one amino acid residue selected from the group consisting of aminoacid residue nos. 6, 21, 22, 24, 25, 27, 28, 31, 32, 35, 39, 41, 42,is/are substituted by any non-helix breaking amino acid residue, theamino acid residue numbering referring to amino acid residues in SEQ IDNO: 7. All these residues have been shown not to be directly involved inthe intermolecular interactions which stabilises the trimeric complexbetween three TTSEs of native tetranectin monomers and it is thereforeexpected that these amino acids may be safely substituted with any aminoacid which will not have an adverse effect on helix formation (notablyproline, which introduces a rigid bend in a polypeptide chain).

Another advantageous embodiment of the monomer polypeptide construct ofthe invention is one which is free from any free amino and/or carboxygroups. This would favour synthesis of a TTSE by means of solid orliquid phase peptide synthesis, since there would be no need ofintroducing any protective groups during peptide synthesis.

Since the consensus sequence of FIG. 2 is believed important and sincethis consensus sequence embraces the above-discussed heptad repeat, itis according to the invention preferred that the TTSE comprises arepeated heptad having the formula a-b-c-d-e-f-g (N to C), whereinresidues a and d generally are hydrophobic amino acids. However, since“a” and “d” in the third of the complete heptads of all known members ofthe tetranectin family are constituted of glutamine, it is mostpreferred that the TTSE comprises the heptad repeated 3 times and thatthe last occurrence of the heptad has a glutamine residue correspondingto residues a and d.

Since exon 2 of native members of the tetranectin family seems tocontain the necessary elements to effect stable trimerisation, it ispreferred that the monomer polypeptide construct is free of substantialparts of tetranectin which is encoded by exon 3 and/or lacks substantialparts of tetranectin which is encoded by exon 1. However, since exon 1encoded material seems to stabilise the trimeric native tetranectin, itis especially preferred that all or part of exon 1 is part of themonomer polypeptide construct, and it also seems to be rational toinclude the first three amino acids encoded by exon 3, since these areknown to take part of the formation of the native triple alpha helicalcoiled coil in human tetranectin.

One particularly interesting embodiment of the invention is thepossibility of designing oriented molecular assemblies, where one ormore functional entities are located N-terminally to the trimerisingelement and one or more functional entities are located C-terminally tothe element. Such types of design may be particularly advantageous wherea certain relative ratio is desired among the different functionalentities included in a specific molecular unit. Such type of design mayin addition be used if one or more functional entities for eitherstructural or functional reasons appear incompatible within the sameconstruct. Such may be the case if one or more of the functionalentities are expressed by large or bulky protein domains which forsteric reasons might prevent formation of the trimeric molecular unitdue to sterical constraints.

The possibility of constructing bi-polar three-way fusion proteins inwhich one functionality is placed N-terminally to the coiled coilstructure and a different functionality is placed C-terminally isadditionally advantageous in applications where large spatial separationbetween the two functionalities are desirable for optimal function.Examples of such application are e.g. the deployment of binding domains(e.g. antibody-derived binding modules) for recognition and binding tobinding sites located at or close to large structures like cellmembranes in cases where it is advantageous to allow for binding of theother end of the trimerised molecule to a different, but also bulkytarget.

Hence, as discussed above, the oligomers of the invention may be used tojoin e.g. bulky surfaces by the oligomer according to the inventioncomprising at least one heterologous moiety which is positionedN-terminally to a TTSE and at least one heterologous moiety which ispositioned C-terminally to a TTSE. The two heterologous moieties can beeither part of the same monomer polypeptide construct or parts of twoseparate monomer polypeptide constructs.

The extraordinarily high stability of any trimer containing thetetranectin trimerisation module under physiological buffer andtemperature condition (i.e. absence of denaturant, temperature notexceeding 40° C.) in combination with the ease by which exchange ofmonomer subunits between trimers can be effected by incubation atmoderately elevated temperature or in the presence of denaturantsprovide for a unique opportunity to deploy the trimerisation module as avehicle to allow the construction of “pick-and-mix” conjugates preparedfrom previously fabricated collections of homotrimeric molecules. Toillustrate the versatility of this design opportunity by way oftheoretical example, let us assume that (1) a collection of twentydifferent antibody constructs (e.g. in the format of single-chain Fv)each of its own characteristic binding specificity, has been selectedand then turned into homo-trimeric molecules by fusion to a tetranectintrimerisation module, and let us also assume that a set of twentydifferent effector molecules (e.g. toxin domains) have similarly beenprepared and also conjugated to the tetranectin trimerisation module. Auser provided with prefabricated collections of twenty differentantibody constructs and twenty different toxin constructs—40 differentreagents in all—has the opportunity then to prepare 400 differenttoxin-antibody conjugates, simply by mixing a first preferred componentfrom one reagent collection with a second preferred reagent from theother collection and then subject this binary mixture to conditions,i.e. gentle heating or incubation with a suitable level of denaturant,to accomplish subunit exchange among all trimeric molecular species inthe mixture. After the subunit exchange step the desiredhetero-bifunctional reagent will be present in the mixture as a majorcomponent of the mixture and may then be deployed as such to accomplisha given purpose or, alternatively apply a simple purification step toisolate his favoured hetero-functional binary reagent from any remainingmono-functional trimer species by a simple standard protein purificationstep, easily designed using standard techniques known in the field ofprotein purification.

A further enhancement of the versatility of the “pick-and-mix”technology may be achieved by including a specific affinity purificationtag on each array of trimerisation module—probe/effector/indicatorconjugate, fused directly in-line or, alternatively, fused via acleavable linker (a polypeptide segment containing e.g. a factor X_(a)or an enterokinase recognition/cleavage site) to the affinity tag. Morespecifically, if each of three libraries were tagged with affinityhandles a, b and c, respectively, that were recognised by bindingsubstances A, B and C, respectively, pure heterotrimers, composed of onemember of each library, could be obtained in a three-step affinitypurification procedure designed to allow selective recovery of only suchtrimers that exhibit affinity for substances A and B and C. If, for anyreason, subsequent removal of the affinity tags were desirable, and theconstructs had been prepared to include cleavable linkers, isolation ofthe pure heterotrimer, liberated from all affinity tags, could beaccomplished by three further affinity purification steps, arranged toisolate only material that would bind to neither substance A norsubstance B nor substance C.

Obviously, the scope of “pick-and-mix” design of user-preparableheterofunctional complexes apply not only to the formation of binaryhetero-functionality, but would apply by logic extension to theformation of ternary hetero-functionality: To envisage the wealth ofpossibilities that are inherent to the concept of ternaryhetero-functionality in a further theoretical example along the linesgiven above, three sets of reagent collections, each comprising 20different functional characteristics, i.e. a collection of in toto 60different homotrimers would allow “pick-and-mix” preparation of 8,000different tri-functional molecules.

The basic tetranectin trimerisation module will, essentiallyindiscriminately, form homo- and hetero-trimers with any molecule thatalso contains a trimerisation module. For some applications it may beadvantageous to have available specially engineered derivatives of thetetranectin trimerisation module, which have been reengineered todisallow homo-trimer formation and hence only allowhetero-trimerisation. Thus, an important embodiment of the monomerpolypeptide construct of the invention is constructed/reengineered so asto disfavour formation of complexes between identical TTSEs; this alsohas the implication that oligomers of the invention can advantageouslybe comprised of monomer polypeptide constructs which are designed so asto disfavour formation of trimers including two monomer polypeptideconstructs having identical TTSEs. One way of disfavouring the formationof homotremerisation would be by “knobs into holes” mutagenisis.

The design/reengineering may be accomplished by introduction of aminoacid substitution at sites in the polypeptide intimately involved in theformation and stability of the trimer and, simultaneously, in adifferent construct introduce a compensatory amino acid substitution,all in all removing symmetry between individual monomer components ofthe triple helical structure so that the structural complementarityprofile only allows the formation of hetero-trimers, but is incompatiblewith some or each of the homotrimer species.

A yet different way to deploy the tetranectin trimerisation module as avehicle to accomplish rational formation of bifunctionalisation wouldrequire the interconnection of the C-terminus of one monomer to theN-terminus of a second monomer in the triple-helical structure. Thebasic requirement for such an intervening polypeptide is, that allowedspatial distances between its N- and C-termini must be compatible withthe spacing inherent to the structural requirements given by thearchitecture of the tetranectin trimerisation module. The constructionof an intervening connecting polypeptide allowed according to suchcriteria would be readily accomplished by an average person skilled inthe art of protein engineering, as an ample collection of examples ofthe deployment of, usually flexible, spacer sequences are known both innature and in designed proteins. Due to the expected entropiccontribution to interaction energy in a molecule in which two of thethree tetranectin trimerisation module components are covalently tiedtogether, such a molecule would show great preference for selecting anymolecule containing only a single copy of the tetranectin trimerisationmodule component, as this selection would be energetically favoured.Hence, conjugation of one functional protein component to a suitablyselected covalently dimerised tetranectin trimerisation module componentand conjugation of a different functional protein component to asingle-copy element of the trimerisation sequence would provide for thepreferential formation of a 1:1 bifunctional complex and suppression offormation of any other complex.

The monomers of the invention may be prepared by methods generally knownin the art, using exclusively or in combination the techniques ofrecombinant protein production, peptide synthesis (liquid phase or solidphase), and traditional chemical coupling of heterologous moieties to apeptide chain or to specific residues therein. Hence the invention alsorelates to a method of preparing the monomer polypeptide construct ofthe invention, the method comprising

-   -   isolating the monomer polypeptide construct from a culture        comprising a host cell which carries and expresses a nucleic        acid fragment which encodes the monomer polypeptide construct,    -   synthesizing, by means of chemical peptide synthesis, the        monomer polypeptide construct and subsequently isolating the        monomer polypeptide construct from the reaction mixture,    -   preparing a TTSE in a culture comprising a host cell which        carries and expresses a nucleic acid fragment which encodes the        TTSE, subsequently linking covalently at least one heterologous        moiety to the TTSE, and thereafter isolating the resulting        monomer polypeptide construct, or    -   synthesizing, by means of chemical peptide synthesis, a TTSE,        subsequently linking covalently at least one heterologous moiety        to the TTSE, and thereafter the isolating the resulting monomer        polypeptide construct from the reaction mixture,        and optionally subjecting the monomer polypeptide construct to        further processing.

The nucleic acid fragment which is mentioned above is also a part of theinvention and is defined as a nucleic acid fragment in isolated formwhich encodes a TTSE as defined herein or which encodes the polypeptidepart of a monomer polypeptide construct according to the invention, withthe proviso that the nucleic acid fragment is different from one thatencodes native members of the tetranectin family, and that the nucleicacid fragment is different from one that encodes any of the fusionproteins CIIH6FXTN123, H6FXTN123, H6FXTN12, H6FXTN23, the sequences ofwhich are shown in SEQ ID NOs: 24-27.

The above mentioned host cell (which is also a part of the invention)can be prepared by traditional genetic engineering techniques whichcomprises inserting a nucleic acid fragment (normally a DNA fragment)encoding the polypeptide part of a monomer polypeptide construct of theinvention into a suitable expression vector, transforming a suitablehost cell with the vector, and culturing the host cell under conditionsallowing expression of the polypeptide part of the monomer polypeptideconstruct. The nucleic acid fragment encoding the polypeptide may beplaced under the control of a suitable promoter which may be inducibleor a constitutive promoter. Depending on the expression system, thepolypeptide may be recovered from the extracellular phase, the periplasmor from the cytoplasm of the host cell.

Suitable vector systems and host cells are well-known in the art asevidenced by the vast amount of literature and materials available tothe skilled person. Since the present invention also relates to the useof the nucleic acid fragments of the invention in the construction ofvectors and in host cells, the following provides a general discussionrelating to such use and the particular considerations in practisingthis aspect of the invention.

In general, of course, prokaryotes are preferred for the initial cloningof nucleic sequences of the invention and constructing the vectorsuseful in the invention. For example, in addition to the particularstrains mentioned in the more specific disclosure below, one may mentionby way of example, strains such as E. coli K12 strain 294 (ATCC No.31446), E. coli B, and E. coli X 1776 (ATCC No. 31537). These examplesare, of course, intended to be illustrative rather than limiting.

Prokaryotes are also preferred for expression, since efficientpurification and protein refolding strategies are available. Theaforementioned strains, as well as E. coli W3110 (F-, lambda-,prototrophic, ATCC No. 273325), bacilli such as Bacillus subtilis, orother enterobacteriaceae such as Salmonella typhimurium or Serratiamarcesans, and various Pseudomonas species may be used.

In general, plasmid vectors containing replicon and control sequenceswhich are derived from species compatible with the host cell are used inconnection with these hosts. The vector ordinarily carries a replicationsite, as well as marking sequences which are capable of providingphenotypic selection in transformed cells. For example, E. coli istypically transformed using pBR322, a plasmid derived from an E. colispecies (see, e.g., Bolivar et al., 1977). The pBR322 plasmid containsgenes for ampicillin and tetracycline resistance and thus provides easymeans for identifying transformed cells. The pBR plasmid, or othermicrobial plasmid or phage must also contain, or be modified to contain,promoters which can be used by the microorganism for expression.

Those promoters most commonly used in recombinant DNA constructioninclude the B-lactamase (penicillinase) and lactose promoter systems(Chang et al., 1978; Itakura et al., 1977; Goeddel et al., 1979) and atryptophan (trp) promoter system (Goeddel et al., 1979; EPO Appl. Publ.No. 0036776). While these are the most commonly used, other microbialpromoters have been discovered and utilized, and details concerningtheir nucleotide sequences have been published, enabling a skilledworker to ligate them functionally with plasmid vectors (Siebwenlist etal., 1980). Certain genes from prokaryotes may be expressed efficientlyin E. coli from their own promoter sequences, precluding the need foraddition of another promoter by artificial means.

In addition to prokaryotes, eukaryotic microbes, such as yeast culturesmay also be used. Saccharomyces cerevisiase, or common baker's yeast isthe most commonly used among eukaryotic microorganisms, although anumber of other strains are commonly available. For expression inSaccharomyces, the plasmid YRp7, for example, is commonly used(Stinchcomb et al., 1979; Kingsman et al., 1979; Tschemper et al.,1980). This plasmid already contains the trpl gene which provides aselection marker for a mutant strain of yeast lacking the ability togrow in tryptophan for example ATCC No. 44076 or PEP4-1 (Jones, 1977).The presence of the trpl lesion as a characteristic of the yeast hostcell genome then provides an effective environment for detectingtransformation by growth in the absence of tryptophan.

Suitable promoting sequences in yeast vectors include the promoters for3-phosphoglycerate kinase (Hitzman et al., 1980) or other glycolyticenzymes (Hess et al., 1968; Holland et al., 1978), such as enolase,glyceraldehyde-3-phosphate dehydrogenase, hexokinase, pyruvatedecarboxylase, phosphofructokinase, glucose-6-phosphate isomerase,3-phosphoglycerate mutase, pyruvate kinase, triosephosphate isomerase,phosphoglucose isomerase, and glucokinase. In constructing suitableexpression plasmids, the termination sequences associated with thesegenes are also ligated into the expression vector 3′ of the sequencedesired to be expressed to provide polyadenylation of the mRNA andtermination.

Other promoters, which have the additional advantage of transcriptioncontrolled by growth conditions are the promoter region for alcoholdehydrogenase 2, isocytochrome C, acid phosphatase, degradative enzymesassociated with nitrogen metabolism, and the aforementionedglyceraldehyde-3-phosphate dehydrogenase, and enzymes responsible formaltose and galactose utilization. Any plasmid vector containing ayeast-compatible promoter, origin of replication and terminationsequences is suitable.

In addition to microorganisms, cultures of cells derived frommulticellular organisms may also be used as hosts. In principle, anysuch cell culture is workable, whether from vertebrate or invertebrateculture. However, interest has been greatest in vertebrate cells, andpropagation of vertebrate in culture (tissue culture) has become aroutine procedure in recent years (Tissue Culture, 1973). Examples ofsuch useful host cell lines are VERO and HeLa cells, Chinese hamsterovary (CHO) cell lines, and W138, BHK, COS-7 293 and MDCK cell lines.

Expression vectors for such cells ordinarily include (if necessary) anorigin of replication, a promoter located in front of the gene to beexpressed, along with any necessary ribosome binding sites, RNA splicesites, polyadenylation site, and transcriptional terminator sequences.

For use in mammalian cells, the control functions on the expressionvectors are often provided by viral material. For example, commonly usedpromoters are derived from polyoma, Adenovirus 2, and most frequentlySimian Virus 40 (SV40). The early and late promoters of SV40 virus areparticularly useful because both are obtained easily from the virus as afragment which also contains the SV40 viral origin of replication (Fierset al., 1978). Smaller or larger SV40 fragments may also be used,provided there is included the approximately 250 bp sequence extendingfrom the HindIII site toward the BglI site located in the viral originof replication. Further, it is also possible, and often desirable, toutilize promoter or control sequences normally associated with thedesired gene sequence, provided such control sequences are compatiblewith the host cell systems.

An origin of replication may be provided either by construction of thevector to include an exogenous origin, such as may be derived from SV40or other viral (e.g., Polyoma, Adeno, VSV, BPV) or may be provided bythe host cell chromosomal replication mechanism. If the vector isintegrated into the host cell chromosome, the latter is oftensufficient.

Upon production of the polypeptide monomer constructs it may benecessary to process the polypeptides further, e.g. by introducingnon-proteinaceous functions in the polypeptide, by subjecting thematerial to suitable refolding conditions (e.g. by using the generallyapplicable strategies suggested in WO 94/18227), or by cleaving offundesired peptide moieties of the monomer (e.g. expression enhancingpeptide fragments which are undesired in the end product).

In the light of the above discussion, the methods for recombinantlyproducing the monomer polypeptide construct of the invention are also apart of the invention, as are the vectors carrying and/or being capableof replicating the nucleic acids according to the invention in a hostcell or a cell-line. According to the invention the expression vectorcan be e.g. a plasmid, a cosmid, a minichromosome, or a phage.Especially interesting are vectors which are integrated in the hostcell/cell line genome after introduction in the host.

Another part of the invention are transformed cells (useful in theabove-described methods) carrying and capable of replicating the nucleicacid fragments of the invention; the host cell can be a microorganismsuch as a bacterium, a yeast, or a protozoan, or a cell derived from amulticellular organism such as a fungus, an insect cell, a plant cell,or a mammalian cell. Especially interesting are cells from the bacterialspecies Escherichia, Bacillus and Salmonella, and a preferred bacteriumis E. coli.

Yet another part of the invention relates to a stable cell lineproducing the polypeptide part of a monomer polypeptide constructaccording to the invention, and preferably the cell line carries andexpresses a nucleic acid of the invention.

On the basis of the above discussions it will be clear to the skilledperson that also the oligomers resulting from the complex formationbetween the monomer constructs of the invention are important parts ofthe invention. Hence the invention also pertains to an oligomer which iscomprised of two monomer polypeptide constructs according to theinvention which comprises at least three TTSEs, or which is comprised ofthree monomer polypeptide constructs according to the invention whicheach only contain one single TTSE.

As is explained herein and shown in the examples, the oligomers of theinvention are stable at temperatures up to 70° C. and it is thereforeespecially preferred that the oligomers of the invention are stable attemperatures above physiological ones, e.g. that the oligomers arestable in the temperature range 50-70° C.

Also a part of the invention is a method for preparing a dimericoligomer of the invention which comprises

-   -   admixing a monomer polypeptide construct which includes two        TTSEs (construct 1) with a monomer polypeptide construct which        includes only one TTSE (construct 2),    -   effecting the two TTSE's of construct 1 to complex with the TTSE        of construct 2 (this can be done by thermal treatment, i.e.        heating to a temperature which ensures denaturation followed by        subsequent cooling allowing renaturation, or this can be done by        denaturing/renaturing effected by changes in the chemical        environment), and    -   isolating the resulting dimer and optionally subjecting the        dimer to further processing (cf. the above discussion of further        processing, but it should also be mentioned that the further        processing could include non-covalent coupling of interesting        and relevant moieties to the dimeric oligomer).

Consequently, the method for producing a trimeric oligomer is also apart of the invention and comprises the steps of

-   -   admixing three monomer polypeptide constructs of the invention        with each other,    -   effecting complex formation between one TTSE of each monomer        polypeptide construct, and    -   isolating the resulting trimer and optionally subjecting the        trimeric oligomer to further processing.

The considerations applying to complex formation and further processingmentioned above apply to this method also.

In view of the detailed discussion above of the “pick-and-mix” aspect ofthe invention, the invention also pertains to a kit comprising

-   -   a first package comprising at least one container means, each at        least one container means containing a monomer polypeptide        construct of the invention,    -   a second package comprising at least one container means, each        at least one container means in the second package containing a        monomer polypeptide construct of the invention, the second        package being different from the first package with respect to        choice and/or number of monomer polypeptide constructs included        therein, and optionally    -   a third package comprising at least one container means, each at        least one container means in the third package containing a        monomer polypeptide construct of the invention, the second        package being different from the first and second packages with        respect to choice and/or number of monomer polypeptide        constructs included therein.

It is preferred that the at least one container means in each packagecontains mutually distinct monomer polypeptide constructs, and it isespecially preferred that all container means comprised in the kitcomprises mutually distinct polypeptide constructs.

A very important aspect of the invention is the possibility ofgenerating a system designed especially for the individualcircumstances. The basic idea is that the artificial selection ofheterologous moieties and optionally active components, and functionalentities result in a unique system as will be further disclosed in thefollowing.

Using the TTSE as a vehicle for assembling monovalent scFv or Fabantibody fragments into oligomeric and multivalent entities offer designadvantages also in terms of generating chimaeric artificial antibodieshaving desirable pharmacokinetic and pharmacodynamic properties. Smallderivatives like monomeric scFv fragments or bivalent “minibodies” arerapidly cleared from the circulatory system, whereas complete Igs stayfor very much longer. Conversely, small derivatives like scFv andminbodies exhibit better extravasation properties. It is thereforeexpected that antibodies of a desired specificity may be optimized forparticular diagnostic or therapeutic needs by engineering thepharmacological properties, using the TTSE as a vehicle for controlledoligomerization of e.g. scFv fragments.

One example of such engineering would be the requirements for deliveringa high dose of an imaging or toxin-conjugated antibody to a tumour,while ensuring as low a systemic exposure or imaging background aspossible. In such case a TTSE conjugated scFv fragment could be designedto exhibit strong multivalent binding to the tumour and rapid clearanceof excess conjugate from circulation.

Accordingly, in af further aspect the present invention also relates tothe use of a monomer polypeptide construct or to a an oligomer accordingto the present invention as a vehicle for assembling antibody fragmentsinto oligomeric or multivalent entities for generating chimericartificial antibodies having preselected pharmacokinetic and/orpharmadynamic properties.

The use of specific delivery systems also play an important role inconnection with the present invention in that such systems may byutilized with respect to different use of the present invention bothwith respect to the a more general therapeutic application and withrespect to gene therapy. Examples of suitable drug delivery andtargeting systems are disclosed in Nature 392 supp. (30 Apr. 1998).

Accordingly, efficiency of deliverance may be further increased if thedelivery system e.g a liposome is supplied with a molecular unit, an“infector or transfector” ligand, recognized by a internalizing receptorunit specific for the target cells. For example, cells displayingendocytotic receptors like members of the LDL family of receptors may beeven more efficiently infected or transfected either by including a TTSEunit in the antibody containing heteorimer or in an independent TTSEunit conjugated to one or more of the domains of the Receptor AssociatedProtein, RAP, (Ellgaard, L., Holtet, T. L., Nielsen, P. R., Etzerodt,M., Gliemann, J. & Thøgersen, H. C. Eur J Biochem. 1997, vol 244,544-551) which is recognized as a ligand to all receptors in thisabundant family of endocytosis-mediating receptors.

Accordingly, in a further aspect, the invention is directed to the useof a monomer polypeptide construct or to an oligomer according to theinvention for targeted gene therapy involving selective delivery of thematerial for transfection or infection of the specific population ofcells.

The ultimate perspective of such TTSE-mediated gene therapy would be thedeployment of a viral vector that would find no other targets in thepatient but the cells displaying the artificial receptor complex.

In a still further aspect, the invention is directed to the use of amonomer polypeptide construct or to a an oligomer construct according tothe invention wherein the at least one heterologous moiety comprises amoiety selected from a ligand binding structure such as a receptormolecule or the ligand binding part of a receptor molecule, and whereinthe gene therapy involves the delivery of nucleic acids to the desiredpopulation of cells by use of a viral vector directed to cellsdisplaying the artificial receptor complex corresponding to theheterologous moiety.

In another aspect, the invention is directed to the use of a monomerpolypeptide construct or to a an oligomer construct according to theinvention wherein at least one TTSE is modified with a membraneintegrating or associating entity having affinity to the specificpopulation of cells in the body relevant for the gene therapy.

Furthermore, a recent review of the imaging an therapeutic potential ofa range of known antibody derivatives has been published by Paul Carterand Margaret Merchant of Genentech Inc. (Current Opinion inBiotechnology, 1997, vol 8, 449-454). In direct continuation of theirconclusions it will be apparent that oligomersation of antibodyderivatives like scFv derivatives may extend current technology in thedesigner-antibody field in many important aspects, some of which will beelaborated below (with reference to the Carter & Merchant review).

One of the well-known problems inherent to mouse monoclonal antibodiesthat have been ‘humanized’ by grafting of the murine antigen combiningsite onto a human Ig framework is that antigenicity of the chimaericproduct in human patients is often difficult to suppress entirely,resulting in—sometimes life-threatening—immune reactions to thediagnostic or therapeutic humanized antibody product. The risk of suchside-effects are expected to be much reduced if the designer antibody isassembled from purely human proteins or protein fragments. Since theTTSE trimerising unit described here is identical to a portion of humantetranectin that is already present in human plasma and tissue, there isgood reason to expect that the TTSE will not elicit an antigenicresponse in a human subject if it is introduced as a component of achimaeric product that is not otherwise antigenic in humans.

Accordingly, in one aspect, the present invention relates to the use ofa monomer polypeptide construct or to a an oligomer according to thepresent invention as a component of a chimaeric product having lowantigenicity in humans relative to formulations comprising on or morecomponents of non-human origin.

Carter & Merchant further review present technology for radiolabellingof antibody derivatives. Again, oligomerisation using TTSEs offer moreelegant solutions to problems associated with labelling, as the TTSEoffers the possibility to construct one or two of the TTSE monomer unitsin a heterotrimeric complex to harbour the site carrying the label.Thus, in this format labelling may also be confined to the non-antibodypart of the complex, leaving the antigen-binding module entirelyunmodified, and the complex may furthermore be formulated “in the field”as and when needed.

In many receptor-mediated signal transduction pathways signals aretriggered by the clustering of receptor molecules on the cell membrane.The TTSEs therefore have important applications in the study andexploitation of receptor signalling, as ligands may be presented asoligomers by conjugation to a TTSE unit.

This also has important application in phage display technologies fordiscovering new ligands and new receptors as the engineering of a TTSEunit fused inline to a candidate ligand molecule will allow the displayof a hetero-trimeric phage coat protein, in which only one of themonomer units is conjugated to the phage coat protein. This may beaccomplished by appropriate insertion of amber codons at the site offusion of phage coat protein to the TTSE-ligand segment of the three-wayfusion protein encoded by the recombinant phage. In appropriate E. colicells the presence of this amber codon will result in translationtermination in the majority of read-throughs, and hence most of thefusion protein product secreted to the periplasmic compartment in thephage-infected bacterium will be soluble TTSE-ligand fusion protein,whereas a minority of the fusion protein will also contain a phageprotein module. The majority of trimers that will be generated willtherefore contain, at most, one monomeric unit that will ensureintegration (display) in the mature recombinant phage particle.

A further advantage of the display technology described above relates tothe fact that it is specially useful for selection on the basis of arelatively low affinity because of the entropic benefit contributionobtained by the proximity of the tree binding moieties in confinedspatial arrangement.

Accordingly, the present invention in an important aspect, also relatesto protein library technology wherein the TTSE's described above areutilized.

The trimerisation of candidated recombinant ligands is especiallyimportant as, for many receptors, the intracellular signal is induced byreceptor clustering, which is only brought about if the external ligandexhibits multivalent binding to the receptor, so as to bridge two ormore receptor molecules.

In one preferred embodiment the monomer polypeptide construct or theoligomer construct according to the invention is for targeted genetherapy involving selective delivery of the material for transfection orinfection of the specific population of cells. The at least oneheterologous moiety may comprise a moiety selected from a ligand bindingstructure such as a receptor molecule or the ligand binding part of areceptor molecule, and wherein the gene therapy involves the delivery ofnucleic acids to the desired population of cells by use of a viralvector directed to cells displaying the artificial receptor complexcorresponding to the heterologous moiety.

As mentioned above, it is an important aspect of the invention that themonomer polypeptide construct and/or the oligomer may be used as acomponent of a chimaeric product having low antigenicity in humans. Asthe construct is of human origin it is believed that the antigenicity inhumans is low relative to formulations comprising on or more componentsof non-human origin.

One primary use of a monomer polypeptide construct or a an oligomeraccording to the invention is for delivering an imaging ortoxin-conjugated antibody to a target such as a tumor, or use as avehicle delivering an substance to a target cell or tissue, as a vehiclefor assembling antibody fragments into oligomeric or multivalententities for generating chimeric artificial antibodies havingpreselected pharmacokinetic and/or pharmadynamic properties.

The substance in question being one or more selected from the group ofheterologous moieties as well a pharmaceutical. Also a labelledconstruct wherein the label is coupled to one or to of the TTSE monomerunits is within the scope of the invention.

As explained in detail previously, an important and surprising use ofthe monomer polypeptide construct or the oligomer according to thepresent invention is for protein library technology, such as phagedisplay technology. The present invention also relates to anypolynucleotide molecule such as a RNA, DNA or PNA as well as any vectorencoding one or more TTSE.

A further use according to invention includes preparation and use of apharmaceutical composition comprising the TTSE construct and optionallya pharmaceutically acceptable excipient. The composition may beadministered by a route selected from the group consisting of theintraveneous route, the intraarterial route, the transmembranes route ofthe buccal, anal, vaginal or conjunctival tissue, the intranasal route,the pulmonary route, the transdermal route, the intramuscular routed,subcutaneous route, intratechal route, inoculation into tissue such as atumour, or by an implant.

The monomer polypeptide construct or the oligomer is in a preferredembodiment comprised in a liposome.

It is obvious from the disclosure of the present invention that thetreating or preventing of a disease may by a further aspect comprisingadministering to the subject in need thereof an effective amount of apharmaceutical composition referred to above.

In one aspect of the various possibilities according to the presentinvention concerning how the human gene therapy is targeted, includesthe case wherein at least one TTSE is modified with a membraneintegrating or associating entity having affinity to the specificpopulation of cells in the body relevant for the gene therapy.

As used in the conventional pharmaceutic field the present inventionincludes a method wherein the monomer polypeptide construct or theoligomer is administered by a route selected from the group consistingof the intraveneous route, the intraarterial route, the transmembranesroute of the buccal, analog vaginal tissue, intranasal route, thepulmonary route, the transdermal route, intramuscular, subcutaneous,intratechal, the buccal, inoculation into tissue such as a tumour, or byan implant.

Finally, the present invention is also relating to the field ofdiagnosing as the skilled person would easily recognize, that the TTSEdisclosed in the present invention may also refer to a method fordiagnosis comprising a construct comprising the monomer polypeptideconstruct or the oligomer, together with a diagnosing component coupledthereon.

Example 1 Design and Construction of the pTH6trip E. coli ExpressionVectors for the Production of Trimerised Chimeric Fusion Proteins

The plasmid clone pT7H6FXTN123 (Example 2) was used as template foramplification in two Polymerase Chain Reactions (PCR) (Saiki et al.,1988) with the primer pairs trip-N (SEQ ID NO: 1) and trip-Ca (SEQ IDNO: 2) and trip-N (SEQ ID NO: 1) and trip-Cb (SEQ ID NO: 3),respectively. The amplified DNA fragments, tripa, comprising nucleotidesequences encoding an IQGR cleavage site for the restriction proteaseFX_(a) (SEQ ID NO: 4) followed by two sites for the restrictionnucleases BglII and KpnI, the nucleotide sequence encoding thetetranectin polypeptide sequence for Glu 1 to Lys 52 (SEQ ID NO: 5)followed by recognition sites for the three restriction endonucleasesBamHI, HindIII, and EcoRI, respectively, and tripb, comprisingnucleotide sequences encoding an IQGR cleavage site for the restrictionprotease FX_(a) (SEQ ID NO: 4) followed by two sites for the restrictionnucleases BglII and KpnI, the nucleotide sequence encoding thetetranectin polypeptide sequence for Glu 1 to Val 49 (SEQ ID NO: 6)followed by recognition sites for the three restriction endonucleasesBamHI, HindIII, and EcoRI, respectively, were subcloned into the plasmidpT7H6 (Christensen et al., 1991), yielding pTtripa and pTtripb,respectively (FIGS. 3 and 4).

Example 2 Tetranectin, Localisation of the Trimerising StructuralElement and Stability of the Triple Alpha Helical Coiled Coil

The cDNA encoding the reading frame corresponding to the maturetetranectin single chain (SEQ ID NO: 7) was cloned by specificamplification in a Polymerase Chain Reaction (PCR) (Saiki et al., 1988)of the nucleotide sequences from amino acid residue Glu1 to Val181 using1^(st) strand oligo-dT primed cDNA synthesized from total humanplacental RNA as template. Primers used in the PCR were SEQ ID NO: 8 andSEQ ID NO: 9. RNA extraction and cDNA synthesis were performed usingstandard procedures. The amplified reading frame encoding the monomersubunit of tetranectin was at the 5′-end, via the PCR-reaction, linkedto nucleotide sequences encoding the amino acid sequence SEQ ID NO: 10which constitute an IEGR cleavage site for the bovine restrictionprotease FX_(a) (Nagai, and Thøgersen, 1987). A glycine residue was, dueto the specific design of the 5′-PCR primer (SEQ. ID NO. 8), insertedbetween the C-terminal arginine residue of the FX_(a) cleavage site (SEQID NO. 10) and the tetranectin Glu1-residue. The amplified DNA fragmentwas subcloned into the E. coli expression vector pT₇H₆ (Christensen etal., 1991) producing the plasmid pT₇H₆FX-TN123 expressing thetetranectin monomer H6FXTN123 (SEQ ID NO: 25) and into pT₇CIIH₆, whichis a derivative of pT₇H₆, where the amino-terminal 32 amino acidresidues of the lambda CII protein (SEQ ID NO. 11) are inserted 5′ ofthe six histidine residues (SEQ ID NO. 12) as outlined in FIG. 5,yielding pT₇CIIH₆FX-TN123 expressing the tetranectin fusion proteinCIIH6FXTN123 (SEQ ID NO: 24). The amino acid sequence of the expressedproteins are shown in FIG. 6 (in SEQ ID NO: 7 is given the amino acidsequence of the mature tetranectin protein). Furthermore threeadditional derivatives of tetranectin were constructed (FIG. 8):H6FXTN12 comprising the tetranectin amino acid residues Glu1 to Val49(SEQ ID NO: 6), H6FXTN23 comprising the tetranectin amino acid residuesVal17 to Val181 (SEQ ID NO: 7), and H6FXTN3 (SEQ ID NO: 30) comprisingthe tetranectin amino acid residues Ala45 to Val181 (SEQ ID NO: 7).These three tetranectin derivatives were constructed by specificamplification in a PCR using pT₇H₆FX-TN123 as template and theprimer-pairs SEQ ID NO: 8 and SEQ ID NO: 13, SEQ ID NO: 14 and SEQ IDNO: 9, and SEQ ID NO: 15 and SEQ ID NO: 9, respectively. The amplifiedDNA fragments were subcloned into the E. coli expression vector pT₇H₆producing the plasmids pT₇H₆FX-TN12, pT₇H₆FX-TN23, and pT₇H₆FX-TN3,respectively (FIG. 7).

To prepare recombinant tetranectin and its derivatives, each of theplasmids pT₇H₆FX-TN123, pT₇CIIH₆FX-TN123, pT₇H₆FX-TN12, pT₇H₆FX-TN23,and pT₇H₆FX-TN3 were grown in medium scale (4×1 liter; 2×TY medium, 5 mMMgSO₄ and 100 μg ampicillin) in E. coli BL21 cells, as described byStudier et al. (1990). Exponentially growing cultures at 37° C. were atOD₆₀₀ 0.8 infected with bacteriophage lambda CE6 at a multiplicity ofapproximately 5. Cultures were grown at 37° C. for another three hoursand the cells harvested by centrifugation.

Cells were resuspended in 150 ml of 0.5 M NaCl, 10 mM Tris-HCl pH 8, and1 mM EDTA pH 8. Phenol (100 ml adjusted to pH 8) was added and themixture sonicated to extract the total protein. Protein was precipitatedfrom the phenol phase by 2.5 volumes of ethanol and centrifugation.

The protein pellet was dissolved in a buffer containing 6M guanidiniumchloride, 50 mM Tris-HCl pH 8 and 0.1 M dithioerythriol. Following gelfiltration on Sephadex G-25 (Pharmacia, Sweden) into 8 M Urea, 1 M NaCl,50 mM Tris-HCl pH 8 and 10 mM 2-mercaptoethanol, the crude proteinpreparation was applied to a Ni²⁺ activated NTA-agarose column(Ni²⁺NTA-agarose, 75 ml pre-washed with 8 M urea, 1 M NaCl, 50 mMTris-HCl pH 8, and 10 mM 2-mercaptoethanol) for purification (Hochuli etal., 1988) and refolding of the fusion proteins, H6FXTN123,CIIH6FXTN123, H6FXTN12, HGFXTN23, and H6FXTN3.

For this study we chose to prepare our own Ni²⁺NTA-agarose matrix. Acarbodiimide coupling of the N-(5-amino-1-carboxypentyl) iminodiaceticacid metal ligand (synthesis route as described by Döbeli & Hochuli(EP-A-0 253 303)) to a rigid agarose matrix (Sepharose CL-6B, Pharmacia,Sweden) was performed:

8 g of N-(5-amino-1-carboxypentyl)iminodiacetic acid from the synthesisprocedure in 50 ml was adjusted to pH 10 by addition of 29 g ofNa₂CO₃(10 H₂O) and added to a stirred suspension of activated SepharoseCL-6B in 1 M Na₂CO₃. Reaction was allowed overnight. The Sepharose CL-6B(initially 100 ml suspension) was activated after removal of water byacetone with 7 g of 1,1′-carbonyldiimidazol under stirring for 15 to 30min. Upon activation the Sepharose CL-6B was washed with acetonefollowed by water and 1 M Na₂CO₃.

The NTA-agarose matrix was loaded into a column and “charged” with Ni²⁺by slowly passing through 5 column volumes of a 10% NiSO₄ solution. Theamount of Ni²⁺ on the NTA-agarose matrix, prepared by this procedure,has been determined to 14 μmol per ml matrix. After charging theNi²⁺NTA-agarose column was washed with two column volumes of water, onecolumn volume of 1 M Tris-HCl pH 8 and two column volumes of loadingbuffer before stirred mixing of the Ni²⁺NTA-agarose matrix with thecrude protein extracts in a breaker for 15 to 30 min. All buffersprepared for liquid chromatography were degassed under vacuum prior toaddition of reductant and/or use.

The Ni²⁺NTA-agarose matrix—crude extract mixture was packed in standardglass columns for liquid chromatography (internal diameter: 2.6 cm) to avolume of approximately 40 ml. The columns were washed with 200 ml of 8M urea, 1 M NaCl, 50 mM Tris-HCl pH 8, and 10 mM 2-mercaptoethanol(Buffer I) and 100 ml 6 M guanidinium chloride, 50 mM Tris-HCl pH 8 and10 mM 2-mercaptoethanol (Buffer II) and the adsorbed tetranectin derivedfusion proteins H6FXTN123, H6CIIFXTN123, H6FXTN23, and H6FXTN3 refoldedusing the cyclic refolding procedure as described (Thøgersen et al., WO94/18227).

The fusion protein H6FXTN12 was refolded by removing the guanidiniumchloride and 2-mercaptoethanol of buffer II in a gradient over 5 columnvolumes into 50 mM Tris-HCl pH 8 and 0.5 M NaCl. After completion of therefolding procedures the tetranectin derived fusion proteins were elutedfrom the Ni²⁺NTA-agarose columns with a buffer containing 0.5 M NaCl, 50mM Tris-HCl, 25 mM EDTA pH 8. The tetranectin fusion proteins H6FXTN123,H6FXTN23, and H6FXTN3 were cleaved with FX_(a) at 4° C. overnight in amolar ratio of 1:300. After FX_(a) cleavage the protein samples wereconcentrated 10 fold by ultrafiltration on YM10 membranes (Amicon).After ten times dilution of the protein sample with 2 mM CaCl₂, therecombinant tetranectin derivatives TN123, TN23, and TN3 were isolatedby ion-exchange chromatography on Q-Sepharose (Pharmacia, Sweden) in alinear gradient over 10 column volumes from 10 mM Tris-HCl pH 8, 2 mMCaCl₂ to 10 mM Tris-HCl pH 8, 2 mM CaCl₂, and 0.5 M NaCl. After elutionfrom the Ni²⁺NTA-agarose columns the fusion proteins H6CIIFXTN123 andH6FXTN12 were likewise concentrated 10 fold by ultrafiltration on YM10membranes and gelfiltrated into buffer containing 25 mM Tris-HCl pH 8,25 mM NaCl, and 2 mM CaCl₂, before purification of correctly foldedmonomer by ion-exchange chromatography on Q-Sepharose as described.

Recombinant full length tetranectin (TN123) produced by these procedureshave been analyzed with respect to binding to plasminogen kringle 4 andimmobilised fucoidan, expression of antigenic sites, and localization ofdisulphide bridges. In all criteria tested the produced TN123 behavedidentically to isolated naturally human tetranectin (data not shown).Furthermore TN123 and TN3 have been crystallized (Kastrup et al., 1996)and the structure has also been determined, all of which bear evidencethat a single unique and biologically active folded product had indeedbeen produced.

Analytical Gelfiltration Analysis of rTN Proteins.

Analytical gelfiltration of the recombinant tetranectin derivativesTN123, TN3, and TN23 (FIG. 9) were performed on a Superose 12 HR 10/30column (Pharmacia, Sweden) with a total volume of 25 ml in 100 mM NaCland 50 mM Tris-HCl pH 8 and a flow rate of 0.2 ml/min. The K_(av) valueis defined by,K _(av)=(Ve−Vo)/(Vc−Vo).

The gelfiltration analysis of TN123 and TN23 show that both proteins areexclusively found as trimers in solution (K_(av) values of 0.27 and0.29, respectively), whereas TN3 appeared monomeric (K_(av): 0.41).

Chemical Cross-Linking of Tetranectin and Derivatives

The recombinant tetranectin derivatives TN123, TN3, and TN23, togetherwith the fusion proteins CIIH6FXTN123 and H6FXTN12 or mixtures of thesederivatives at 1 mg/ml concentrations in cross-linking buffer (0.1 MSodium borate, pH 9.1) were incubated with dimethylsuberimidate (DMSI,Sigma). 10 μl aliquots of protein solution were incubated with 1 μlaliquots of DMSI stock solution (20 mg/ml in cross-linking buffer) for30 minutes at 25° C. before addition of 2 μl quenching buffer (3 MTris-HCl, pH 9). Subunit exchange between pre-formed homo-oligomers wasinduced by subjecting protein mixtures to heat shock treatment. Five μlaliquots of each protein solution (1 mg/ml stocks) were mixed at 0° C.in standard polypropylene microcentrifuge tubes, transferred to a waterbath at 70° C. for the time spans indicated, and then further incubatedfor 15 minutes at 25° C. before reaction with DMSI.

Prior to analysis by SDS-PAGE (12% gels) of the cross-linked productsthe reaction samples were boiled in the presence of SDS andmercaptoethanol.

Cross-linking analysis of TN123 and the fusion protein CIIH6FXTN123showed that no detectable subunit exchange between pre-formedhomo-oligomers in a mixture of TN123 and CIIH6FXTN123 was found after 16hours at room temperature (FIG. 10). Subunit exchange could be inducedby incubating the protein mixture at 70° C. for 15 seconds or longerbefore cooling to room temperature and addition of DMSI. SDS-PAGEanalysis showed the presence of four trimer bands above 95 kDa(corresponding to two homo-trimers and two hetero-trimers) and threedimer bands (corresponding to two homo-dimers and one hetero-dimer) inthe gel between 43 and 55 kDa, in a relative abundance in agreement withrandom association of monomer subunits into trimers after subunitexchange. It should be noted, that molecular weight markers have onlybeen included on the SDS-PAGE gels for crude calibration and orientationof the gels.

The trimeric organization of tetranectin was further corroborated bycross-linking studies of the proteins H6FXTN12, TN23, and TN3 andmixtures between them (FIG. 11). The tetranectin derivative TN3,containing only the CRD, could not be cross-linked even at high proteinconcentrations and did not interfere with the cross-linking of rTN123.Likewise, the derivative TN23, containing exon 2 and the CRD, appearedmonomeric after cross-linking and was found not to interfere withtrimerisation of TN123 during subunit exchange. Dimeric TN23 moleculesfound at low abundance in the sample probably reflects contaminatingmisfolded disulphide bridged dimers. The fusion protein H6FXTN12 formedhomo-trimers upon cross-linking and generated hetero-trimers with TN123after subunit exchange. Because of the difference in size of full lengthtetranectin (TN123) and H6FXTN12 the possible nine protein bandsresulting from chemical cross-linking are: The four trimers [(TN123)₃,(TN123)₂ (H6FXTN12), (TN123)(H6FXTN12)₂, and (H6FXTN12)₃] at approx. 95kDa, 50 kDa, 37 kDa, and 20 kDa, respectively; the three dimers[(TN123)₂, (TN123)(H6FXTN12), and (H6FXTN12)₂] at approx. 45 kDa, 30kDa, and 15 kDa, respectively; and the two monomers TN123 at 23 kDa andH6FXTN12 at 9 kDa.

Taken together, the gel filtration and the cross-linking analysis of thetetranectin derivatives show that tetranectin, like the collection groupof C-type lectins, is a trimeric molecule and that amino acid residuesdirectly shown to be involved in trimerisation of the tetranectinmonomer are located in exon 2 of the protein (Val17-Val49). Furthermoresubunit exchange between the trimeric molecules could only be observedafter heat denaturation. Amino acid residues Glu1 to Asp16 oftetranectin are critical to chemical cross-linking with DMSI and moreimportant appear to stabilize the trimeric molecule because thecross-linking analysis of the mixture TN123 and TN23 showed no decreasein TN123 formation after heat denaturation and possible subunit exchange(FIG. 11). The stability of the tetranectin trimer was corroborated by across-linking analysis with DMSI at different temperatures. Fifteen μlTN123 at 0.3 mg/ml concentration was pre-incubated 10 min. at either 37°C., 50° C., 60° C., or 70° C. before addition of 2 μl DMSI (20 mg/ml).The reaction was allowed to proceed for 15 min. before reaction wasquenched with 5 μl of 3M Tris-HCl pH 9.1 and the reaction mixturesallowed to cool to room temperature. SDS-PAGE analysis of reducedsamples (FIG. 12) showed, that trimers are readily detectable even at60° C., although a competing pattern of cross-linking specimensincreases at increasing temperatures. The appearance of othercross-linking specimens is probably due to the unfolding of the CRD. Thestability of the tetranectin trimerising structural element is furtheranalyzed using a designed chimeric protein in Example 3.

Example 3 Design and Construction of the Recombinant Chimeric ProteinTRIPB-UB—the Tetranectin Trimerising Structural Element and Ubiquitin

A plasmid clone, pLCMHF/UB, generously provided by Dr. O. Wiborgharbouring a human ubiquitin cDNA insert (SEQ ID: 16) was used astemplate and SEQ ID NO: 17 together with SEQ ID NO: 18 were used foramplification in a Polymerase Chain Reaction (PCR) (Saiki et al., 1988)of the nucleotide sequence encoding amino acid residue Ile1 to Gly76 ofhuman ubiquitin (SEQ ID: 19). The amplified DNA fragment was afterdigestion with the restriction endonucleases BamHI and HindIII ligatedinto the BamHI and HindIII sites of pTtripb (Example 1) yieldingpTtripb-UB (FIG. 13) using standard procedures.

To prepare the chimeric fusion protein H6FXtripb-UB (FIG. 14, SEQ ID NO:31) the plasmid pTtripb-UB was grown in medium scale (4×1 liter; 2×TYmedium, 5 mM MgSO₄ and 100 μg ampicillin) in E. coli BL21 cells, asdescribed by Studier et al. (1990). Exponentially growing cultures at37° C. were at OD₆₀₀ 0.8 infected with bacteriophage lambda CE6 at amultiplicity of approximately 5. Cultures were grown at 37° C. foranother three hours and the cells harvested by centrifugation. Cellswere resuspended in 150 ml of 0.5 M NaCl, 10 mM Tris-HCl pH 8, and 1 mMEDTA pH 8. Phenol 4100 ml adjusted to pH 8) was added and the mixturesonicated to extract the total protein. Protein was precipitated fromthe phenol phase by 2.5 volumes of ethanol and centrifugation. Theprotein pellet was dissolved in a buffer containing 6 M guanidiniumchloride, 50 mM Tris-HCl pH 8 and 0.1 M dithioerythriol. Following gelfiltration on Sephadex G-25 (Pharmacia, Sweden) into 8 M Urea, 1 M NaCl,50 mM Tris-HCl pH 8 and 10 mM 2-mercaptoethanol, the crude proteinpreparation was applied to a Ni²⁺ activated NTA-agarose column forpurification (Hochuli et al., 1988) and refolding of the fusion proteinH6FXtripb-UB.

Synthesis and charging of the Ni²⁺ activated NTA-agarose matrix isdescribed in Example 2. All buffers for liquid chromatography weredegassed prior to use. The fusion protein H6FXtripb-UB was refolded byremoving the urea and 2-mercaptoethanol from buffer II in a gradientover 5 column volumes into 50 mM Tris-HCl pH 8 and 0.5 M NaCl. Aftercompletion of the refolding procedure the H6FXtripb-UB fusion proteinwas eluted from the Ni²⁺NTA-agarose columns with a buffer containing 0.5M NaCl, 50 mM Tris-HCl, 25 mM EDTA pH 8 and gel filtrated on a SephadexG50 column (Pharmacia) into 0.1 M Sodium borate pH 9 buffer for chemicalcross-linking analysis with DMSI.

The cross-linking analysis experiment was designed both to analyze theoligomeric status of the chimeric fusion protein and the thermalstability of the presumed fusion protein trimer as described in Example2: Samples of 15 μl H6FXtripb-UB fusion protein, at approximately 1.0mg/ml concentration, were pre-incubated 10 min. at either 37° C., 50°C., 60° C., or 70° C. before addition of 2 μl DMSI (20 mg/ml). Thereactions were allowed to proceed for 15 min. before quenching byaddition of 5 μl of 3 M Tris-HCl pH9.1 and the reaction mixtures wereallowed to cool to room temperature. SDS-PAGE analysis of reducedsamples (FIG. 12) showed, (1) that the fusion protein H6FXtripb-UB is atrimer in solution (monomer at 17 kDa, dimer at 35 kDa, and trimer at 43kDa) and (2) that a substantial amount of trimer molecules is presenteven at 70° C. The appearance of other larger cross-linking products isprobably due to cross-linking of trimers via the ubiquitin part of thefusion protein.

Example 4 Design and Construction of Trimerised and Hexamerized CEA6scFv Antibodies scFv(CEA6)-TRIPB, TRIPB-scFv(CEA6) andscFv(CEA6)-TRIPB-scFv(CEA6)

A plasmid clone, pUC19MCH/CEA6, generously provided by Dr. KevinPritchard, Cambridge Antibody Technology Ltd., Melbourn, UK, harbouringa nucleotide sequence (SEQ ID: 20) encoding the CEA6 antibody insingle-chain Fv (scFv) format, followed in sequence by a “myc tag”(which is a general purification/detection handle), was used as templatein Polymerase Chain Reactions (PCR) (Saiki et al., 1988) in which thenucleotide sequence encoding the scFv+myc tag was amplified using theprimer pairs (SEQ ID: 21 and SEQ ID: 22) and (SEQ ID: 21 and SEQ ID: 23)to generate PCR fragments “A” and “B”.

PCR fragment “A” was treated with restrictions enzymes BamHI and KpnIand the resulting fragment was inserted into BglII/KpnI cut pTripb(Example 1) to obtain the vector pTH6FXscFv(CEA6)-tripb (FIG. 15)encoding the H6FXscFv(CEA6)-TRIPE fusion protein (FIG. 16). PCR fragment“B” was treated with restriction enzymes BamHI and HindIII and theresulting fragment was inserted into BamHI and HindIII cut pTripb(Example 1) to obtain the vector pTH6FXtripb-scFv(CEA6) (FIG. 17)encoding the H6FXTRIPB-scFv(CEA6) fusion protein (FIG. 18, SEQ ID NO:33) using standard procedures.

To generate the expression vector pTH6FXscFv(CEA6)-tripb-scFv(CEA6)(FIG. 19) encoding the H6FXscFv(CEA6)-TRIPB-scFv(CEA6) fusion protein(FIG. 20, SEQ ID NO: 34) the insert in the vector pTH6FXtripb-scFv(CEA6)was excised using restriction enzymes BamHI and HindIII and insertedinto the vector pTH6FXscFv(CEA6)-tripb, which had been treated withrestriction enzymes BamHI and HindIII.

To prepare the chimeric fusion proteins H6FXscFv(CEA6)-TRIPB (SEQ ID NO:32), H6FXTRIPB-scFv(CEA6) (SEQ ID NO: 33) andH6FXscFv(CEA6)-TRIPB-scFv(CEA6) (SEQ ID NO: 34) the plasmidspTH6FXscFv(CEA6)-TRIPB, pTH6FXtripb-scFv(CEA6) andpTH6FXscFv(CEA6)-tripb-scFv(CEA6) were grown in small scale (1 liter;2×TY medium, 5 mM MgSO4 and 100 μg ampicillin) in E. coli BL21 cells, asdescribed by Studier et al. (1990). Exponentially growing cultures at37° C. were at OD₆₀₀ 0.8 infected with bacteriophage lambda CE6 at amultiplicity of approximately 5. Cultures were grown at 37° C. foranother three hours and the cells harvested by centrifugation. Cellswere resuspended in 50 ml of 0.5 M NaCl, 50 mM Tris-HCl pH 8, and 1 mMEDTA pH 8. Phenol (50 ml adjusted to pH 8) was added to each and themixtures were sonicated to extract total protein. After clarification bycentrifugation (25 minutes at 10.000 g) crude protein fractions wereprecipitated from the phenol phases by addition of 2.5 volumes ofethanol and centrifugation. Protein pellets were dissolved in a buffer(15-25 ml) containing 6 M guanidinium chloride, 50 mM Tris-HCl pH 8 and0.1 M dithioerythriol. Following gel filtration on Sephadex G-25(Pharmacia, Sweden) into 8 M Urea, 1 M NaCl, 50 mM Tris-HCl pH 8 and 10mM 2-mercaptoethanol, the crude protein preparations were applied toNi²⁺ activated NTA-agarose columns (75 ml column volume) forpurification (Hochuli et al., 1988). Washing buffer (6 M guanidine-HCl,50 mM Tris-HCl pH 8 and 10 mM 2-mercaptoethanol) was then flowed throughthe columns until stable baselines were obtained. Virtually pure fusionproteins could then be eluted by applying a pH gradient to each column(1000 ml gradient in 8 M urea and 10 mM 2-mercaptoethanol obtained bylinear (per volume) mixing of solutions containing 50 mM sodiumdi-hydrogenphosphate (pH 5 buffer) and 50 mM di-sodium hydrogenphosphate(pH 8 buffer).

In preparation for in vitro refolding by the method of Thøgersen et al.(WO 94/18227) 20 mg of each purified fusion protein were mixed insuspensions in refolding “buffer B” (described below) with aliquots ofsuspensions of Ni²⁺ activated NTA-agarose matrix sufficient to generatecolumns of about 75 ml packed bed volume. Each fusion protein was thensubjected to the iterative refolding procedure as described forplasminogen kringle 4 in the Thøgersen et al. patent application (WO94/18227), except that refolding of the scFv containing fusion proteinswas carried out at 10° C. using a buffer containing 0.5 M NaCl, 50 mMTris-HCl pH 8, 2 mM glutathione and 0.2 mM oxidized glutathione as“buffer A” and a buffer containing 8 M urea, 1 M NaCl, 50 mM Tris-HCl pH8 and 2 mM glutathione as “buffer B”.

After completion of the refolding procedure each column was washed with300 ml buffer containing 0.5 M NaCl and 50 mM Tris-HCl pH 8 to wash awayglutathione. The refolded fraction of each protein was then eluted fromthe NTA-agarose matrix by addition of 20 mM EDTA to the elution buffer.After addition of solid urea to achieve a final concentration of about 8M to each protein sample and dilution or dialysis to reduce NaClconcentrations to below 5 mM, final purification of each correctlyfolded fusion protein product was then accomplished by ion exchangechromatography (S-Sepharose, Pharmacia, 1.6 (i.d.) by 90 centimetercolumn in a buffer containing 8 M urea, 5 mM Tris-HCl (from 1 M stocksolution at pH 8) and 25 mM sodium acetate (from 1 M stock solution atpH 5), eluted at 2 ml/min). After dialysis against aqueous buffers (e.g.phosphate buffered saline) each pure and correctly refolded fusionprotein was recovered in yields of 2-6 mg per liter of culture grown.Each protein may be shown by analytical gel filtration, chemicalcross-linking analysis, by in vitro affinity measurements and by in vivoefficacy to form a stable homotrimeric molecular complex: The oligomericstatus of the H6FXtripb-scFv-(CEA6) fusion protein was analyzed bychemical cross-linking analysis with DMSI: In parallel experiments,samples of H6FXtripb-scFv-(CEA6) at 0.34 mg/ml and TN123 at 0.28 mg/mlin 0.1 M Sodium borate were incubated at room temperature withincreasing amounts (0-40 μg in 12 μl in total) of DMSI for 30 min.Reactions were quenched by addition of 5 μl 3M Tris-HCl pH 9 and thesamples analyzed by SDS-PAGE under reducing conditions (FIG. 21). Liketetranectin, the H6FXtripb-scFV-(CEA6) fusion protein, of approximately38 kDa, is hereby shown to be a trimer in solution.

REFERENCES

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1. An isolated polypeptide comprising: (a) a first functional amino acidsequence that is capable of forming a trimeric complex with two otherfirst functional amino acid sequences and that has up to five amino acidsubstitutions at positions 10, 17, 20, 21, 24, 25, 26, 28, 29, 30, 31,32, 33, 34, or 35 of the amino acid sequence of SEQ ID NO: 40, whereinthe first functional amino acid sequence is not identical to theconsensus sequence shown in SEQ ID NO: 40; and (b) a second functionalamino acid sequence that is heterologous to the first functional aminoacid sequence.
 2. An isolated polypeptide comprising: (a) a firstfunctional amino acid sequence that is capable of forming a trimericcomplex with two other first functional amino acid sequences, whereinthe first functional amino acid sequence comprises the consensussequence of SEQ ID NO: 40; and (b) a second functional amino acidsequence that is heterologous to the first functional amino acidsequence, wherein the second functional amino acid sequence does notexclusively facilitate expression and/or purification of thepolypeptide; and wherein the first functional amino acid sequence isfused to the second functional amino acid sequence and the isolatedpolypeptide does not consist of the amino acid sequence of SEQ ID NO:27.
 3. The isolated polypeptide of claim 1, wherein the first functionalamino acid has four amino acid substitutions at positions 10, 17, 20,21, 24, 25, 26, 28, 29, 30, 31, 32, 33, 34, or 35 of the amino acidsequence of SEQ ID NO:
 40. 4. The isolated polypeptide of claim 1,wherein the first functional amino acid has three amino acidsubstitutions at positions 10, 17, 20, 21, 24, 25, 26, 28, 29, 30, 31,32, 33, 34, or 35 of the amino acid sequence of SEQ ID NO:
 40. 5. Theisolated polypeptide of claim 1, wherein the first functional amino acidhas two amino acid substitutions at positions 10, 17, 20, 21, 24, 25,26, 28, 29, 30, 31, 32, 33, 34, or 35 of the amino acid sequence of SEQID NO:
 40. 6. The isolated polypeptide of claim 1, wherein the firstfunctional amino acid has one amino acid substitution at any one ofpositions 10, 17, 20, 21, 24, 25, 26, 28, 29, 30, 31, 32, 33, 34, or 35of the amino acid sequence of SEQ ID NO:
 40. 7. The isolated polypeptideof claim 1, wherein the second functional amino acid sequence comprisesan amino acid sequence encoding all or a part of: (a) a ligand bindingstructure; (b) a ligand; (c) a receptor binding structure; (d) areceptor; (e) a detectable moiety; (f) an in situ activatable substance;(g) an enzyme; or (h) a cytokine.
 8. The isolated polypeptide of claim7, wherein the ligand binding structure is a receptor molecule, theligand binding part of a receptor molecule, an antibody, an antigenbinding antibody fragment, a monovalent scFv antibody fragment, a Fabantibody fragment, or a lectin.
 9. The isolated polypeptide of claim 1,wherein the second functional amino acid sequence does not facilitateexpression and/or purification of the polypeptide.
 10. The isolatedpolypeptide of either claim 1 or 2, further comprising a thirdfunctional amino acid sequence that is heterologous to the first aminoacid sequence.
 11. The isolated polypeptide of claim 2, wherein thesecond functional amino acid sequence comprises an amino acid sequenceencoding all or a part of: (a) a ligand binding structure; (b) a ligand;(c) a receptor binding structure; (d) a receptor; (e) an in situactivatable substance; (f) an enzyme; or (g) a cytokine.
 12. Theisolated polypeptide of claim 11, wherein the ligand binding structureis a receptor molecule, the ligand binding part of a receptor molecule,an antibody, an antigen binding antibody fragment, a monovalent scFvantibody fragment, a Fab antibody fragment, or a lectin.
 13. A trimericpolypeptide complex comprising three isolated polypeptides of eitherclaim 1 or
 2. 14. The trimeric polypeptide complex of claim 13, whereinat least two of the second functional amino acid sequences are differentfrom each other.
 15. The trimeric polypeptide complex of claim 13,wherein all three of the second functional sequences are different fromeach other.
 16. The trimeric polypeptide complex of claim 13, whereinthe complex remains as a trimer at a temperature of at least 60° C. 17.The trimeric polypeptide complex of claim 13, wherein the complexremains as a trimer at a temperature of about 70° C.
 18. A method forpreparing the trimeric polypeptide complex of claim 13, comprising: (a)mixing the polypeptides; (b) effecting complex formation between thepolypeptides; and (c) isolating the resulting trimeric polypeptidecomplex.